1. Field of the Invention
The present invention relates to magnetic powder, a method of manufacturing the same, and the usage thereof. More specifically, the present invention relates to magnetic powder modified so as to enhance dispersion in an organic solvent-based magnetic layer-forming coating liquid, a method of manufacturing the same, and the usage thereof.
2. Discussion of the Background
In recent years, the means of rapidly transmitting information have undergone considerable development, permitting the transmission of data and images containing immense amounts of information. With this improvement in data transmission technology has come the demand for higher density recording in recording media and recording and reproduction devices for recording, reproducing, and storing information. The high dispersion of microparticulate magnetic powder and increased smoothing of the surface of the magnetic layer to reduce spacing loss are known to be effective ways of achieving good electromagnetic characteristics in the high-density recording region.
Widely employed methods of enhancing the dispersion of magnetic powders include, for example, the method of incorporating a polar group such as a SO3Na group into a binder that is described in Japanese Unexamined Patent Publication (KOKAI) No. 2003-132531 or English language family members US2003/143323 A1 and U.S. Pat. No. 6,677,036, which are expressly incorporated herein by reference in their entirety, and the method of using a dispersing agent as an additive during the manufacturing of a magnetic layer-forming coating liquid as described in Japanese Unexamined Patent Publication (KOKAI) Heisei No. 1-232530, which is expressly incorporated herein by reference in its entirety.
As described in Japanese Unexamined Patent Publication (KOKAI) No. 2003-132531, incorporating polar groups into a binder is an effective means of enhancing dispersion. Conversely, when the number of polar groups introduced into the binder is excessive, dispersion may decrease. Additionally, dispersing agents such as those described in Japanese Unexamined Patent Publication (KOKAI) Heisei No. 1-232530 adsorb to the surface of magnetic particles and enhance compatibility between the magnetic particles, binder, and solvent, thereby improving dispersion of the magnetic particles in the magnetic layer-forming coating liquid. However, even when a microparticulate magnetic powder of small primary particle diameter is employed, the microparticles of the magnetic powder aggregate strongly, and end up being added to the magnetic layer-forming coating liquid as a coarse aggregate. Unless a powerful dispersion load is applied to break down the aggregated state of the magnetic powder, the dispersing agent does nothing but cover the surface of the aggregate. As a result, the magnetic powder ends up being present in the form of a coarse aggregate in the magnetic layer that is formed, precluding the achievement of good surface smoothness. It would also be conceivable to intensify the dispersing conditions to break down the aggregate formed by the powerful aggregation of microparticles of magnetic powder. However, when that is done, abrasion of the dispersion medium causes foreign matter to mix into the medium and damages the magnetic powder, undesirably presenting the possibility of compromising magnetic characteristics.